High speed automotive type diesel engine



April 15, 1969 L. D. THOMPSON HIGH SPEED AUTOMOTIVE TYPE DIESEL ENGINE Filed July 11. 1966 HN Q any? 0 6 W W WW k M 0m 8 m United States Patent 3,438,327 HIGH SPEED AUTOMOTIVE TYPE DIESEL ENGINE Lionel D. Thompson, Bloomfield Hills, Mich, assignor to Holly Carburetor Company, Warren, Mich, a corporation of Michigan Filed July 11, 1966, Ser. No. 564,276 Int. Cl. F04b 49/08; F04d /00; F02m 39/00 US. Cl. 103-41 18 Claims ABSTRACT OF THE DISCLOSURE A fuel injection pump for a multicylinder engine in tended to idle on less than all its cylinders, the pump including a fuel cylinder for each engine cylinder, each fuel cylinder having a rotatable and reciprocable plunger with a contoured edge inclined with respect to the plunger axis and cooperating with a control port in the fuel cylinder to determine the effective pumping stroke of the plunger, means for reciprocating and rotating the plungers, the control edges for the engine cylinders operating at idle being inclined or contoured so as to supply fuel at engine idle and the control edges for the engine cylinders not operating at idle being inclined or contoured differently so as to gradually reduce fuel at a greater rate on decreasing load until no fuel is supplied thereby at engine idle, the pump, in its preferred embodiment, including an idle governor whereby those engine cylinders operating at engine idle receive more fuel than they would if all engine cylinders were operating at engine idle.

This invention relates generally to diesel engines, and more particularly to means for improving the idle speed operation of multicylinder, high speed, automotive type diesel engines, with particular regard to steadier speed control and decreased exhaust emission.

There is a very definite trend, especially in the truck industry, to replace the gasoline engine with a diesel power plant, and much Work is being done to develop diesel engines that are sufficiently compact and light in weight to satisfy modern automotive requirements. At the same time, of course, urban areas are beset with the so-called smog problem, and the automotive industry is being called upon to reduce engine exhaust emissions. If possible, this must be done without compromising engine performance.

The design approaches employed in this current development aggravate a basic problem common to diesel engines, namely, that of obtaining uniform combustion and regular firing over the necessary wide range of speeds and loads. That is, current automotive diesels are required to provide steady and regular combusion at no-load idle speed, which may be as low as one-eighth the maximum rated speed. The design routes being used to develop such engines, with the weight, size and speed characteristics required for automotive applications include high maximum rated speeds, reduced rotational inertia and increased number of cylinders per engine, all of which aggravate the problem of obtaining steady regular combustion or firing at the low idle, no-load operating condition.

For example, higher maximum rated speeds increase the speed range over which the injection system must accurately meter the fuel. In general, the inherent characteristics of pulsing hydraulic injection systems are such that equipment sized for high flows often performs erratically at the very low speeds and fuel fiows associated with engine idle operation. Also, higher maximum rated speeds increase the variation in air movements (swirl, squish, etc.) encountered by the fuel in the combustion chamber. That is, engines are generally designed so that ice the air movement in the combusion chamber at high speeds and maximum loads matches the fuel injection rates and atomization characteristics and provides smoke free combusion. However, at idle speeds approaching oneeighth maximum speed, the air movement in the same engines usually is far too slow for suitable mixing of the air and fuel. Therefore, to obtain satisfactory combustion at these low loads and low speeds, other factors such as combustion chamber temperature may have to be raised to offset the unsatisfactory air fuel mixing. Higher rated speeds also increase the range of air density and compression pressures over which the engine must perform satisfactorily. Since engines are generally designed to have adequate breathing (air density) and heat of compression pressure at their maximum speed and rating, the same engine, when operated at very low speeds, has a lower compression temperature and air density, making ignition and combustion more difficult and often erratic.

Reducing the rotating inertia means that smaller changes in firing pressures or combustion cause greater fluctuations in engine speed, thus making it more difficult for the engine governor to control or hold the engine at a steady idle no-load speed.

Increasing the number of cylinders per engine further aggravates the no-load idle speed combustion problem because there are more combustion chambers being used to overcome the relatively low idle friction loads; thus, smaller quantities of fuel must be accurately and regularly metered and properly mixed, which is always difficult to accomplish consistently because percent variations are greater.

Accordingly, a main object of this invention is to provide means for offsetting the above mentioned basic detrimental etfects of current trends in the design of modern high speed automotive diesel engines, the basic purpose being to obtain good, regular, no-load idle or low speed combustion. Essentially, the invention involves providing, by a novel and convenient modification of a particular well-known diesel fuel system, means which automatically cuts out completely all fuel to one or more of the engine cylinders for operating parameters such as loads or torques below a predetermined value. This basic principle, which appears to be suggested in Stamsvik 1,898,602 obviously illustrating a nonautomotive type diesel engine and a comple ely dilferent type of fuel system, is particularly suited for high compression diesel engines wherein light load firing pressures are percentagewise very close to the compression pressures of cylinders not obtaining fuel; that is, the nonfiring cylinders are not sufiiciently pressurewise different than the firing cylinders to cause unsatisfactory vibration or unbalance.

As will be explained, cutting out cylinders for reduced load operation raises the combustion chamber temperature of the operating cylinders, thus improving the combustion in the firing cylinders. Cutting out cylinders at reduced load and increasing the quantity of fuel flowing through the injection system for the firing cylinders makes it easier to maintain uniform injection during no-load idle operation. The improved combustion due to higher cylinder temperatures and the more regular and better atomized injection of the fuel in the firing cylinders improves the smoothness of low speed no-load diesel operation and reduces idle exhaust emissions, which reduces wasted fuel and air pollution and increases economy.

The proposed method of cutting out several cylinders to improve combustion, firing regularity and speed control at low load and idle speeds can be illustrated by reference to pages 5, 6 and 7 of the second edition of the book entitled Internal Combustion Engine by Edward F. Obert wherein the type of fuel metering system to which the invention is adapted is described. It will be noted that the quantity of fuel flowing to the engine cylinder depends both on the position of the rack C and the helix edge of the slot B formed in the plunger, it being understood that the term helix edge is a control edge inclined with respect to the plunger axis and not necessarily a true helix. Thus, one way to accomplish the object of this invention, namely cutting out several cylinders to improve combustion, firing regularity and speed control at low load and idle speeds, would be to equip a multicylinder engine with a multiplunger fuel pump wherein rotation of all of the plungers would be controlled by a common rack C. To obtain the desired cutout of several cylinders, it is only necessary to form the desired number of pump plungers with different metering helix or control edge shapes that cutout or stop fuel flow (by reducing the effective pumping stroke) at a rack position that still causes the normal plungers to supply fuel to the other engine cylinders. That is, as the rack which controls all of the pump plungers for a multicylinder engine is moved from the maximum fuel flow position towards the zero flow position, several helices or control edges may be of such a contour, and different from the helices or control edges of the other plungers, so they are at zero flow before the rack travels sufiiciently far to have all cylinders cutoff. At the same time, the common rack C can be repositioned, as compared to a prior art system in which all of the cylinders fire at no-load idle, so that the firing cylinders receive more than the normal fuel so as to maintain idle speed, provide better combustion and reduce emissions. Economy is further achieved by the fact that the additional fuel to four firing cylinders need not be double that which was required for eight firing cylinders, for example.

In summary, then, a main object of the invention is to provide means for improving the no-load idle operation of modern automotive type, multicylinder diesel engines.

Another object of the invention is to accomplish the above result by eliminating the operation of some of the cylinders of a multicylinder automotive type diesel engine during no-load idle operation.

Still another object of the invention is to provide a fuel injection system for such engines that will cut off the fuel to certain engine cylinders under certain operating conditions.

A more specific object of the invention is to provide such a fuel injection system wherein the means for cutting off the fuel to certain engine cylinders is accomplished by forming a different helix angle on the plungers associated with the cylinders to be cut off.

These and other objects and advantages of the invention will become more apparent upon reference to the following specification and the accompanying drawings wherein:

FIGURE 1 is a schematic illustration of a representative prior art V-type, multicylinder, automotive diesel engine subject to the above mentioned problems which can and have been eliminated by incorporating the invention.

FIGURE 2 is an enlarged fragmentary portion of the fuel injection pump shown in FIGURE 1.

FIGURES 3-5 are fragmentary schematic illustrations of a portion of FIGURE 2 illustrating the various phases of operation of one plunger of the pump shown by FIG- URES 1 and 2 in supplying fuel to one cylinder of the prior art multicylinder diesel engine.

FIGURE 6 is similar to FIGURE 5, but illustrating one method by which the invention may be embodied in the type of prior art engine and pump shown.

Referring now to FIGURE 1, the engine 10 comprises an engine block 12 of the V-type containing two rows 14 of cylinders, the engine being partially cut away to illustrate one of the plurality of cylinders 16, the piston 18, the connecting rod 20, the crank shaft 22, the exhaust port 24 and spring loaded exhaust valve 26, the rocker arm 28 and the cam shaft 30 operating the push rod connected to the rocker arm 28. Each cylinder has the usual spring loaded or other nozzle 32 for injecting solid fuel into the usual precombustion chamber 34. The bottom of the block 12 is, of course, closed by an oil pan 36 containing the lubricating oil for splash type lubrication.

As usual, the engine 10 is equipped with a fuel injection pump 38 operated by a cam shaft 40 driven by the engine 10 in a manner similar to the cam shaft 30 that operates the exhaust valves 26. Usually, the pump 38 has one injection plunger or piston 42 for each engine cylinder 16 and the lobes on the cam shaft 40 are arranged so as to coordinate the supply of fuel to the engine cylinders in the proper firing order. A conduit 44 leading from each nozzle 32 to each plunger 42 may be controlled by a spring loaded check valve 46, and each plunger 42 is loaded downwardly in the suction stroke by a spring 48 and urged upwardly in the pump stroke by a lobe on the cam shaft 40. The usual method of injection is to compress and spray solid fuel into each cylinder 16 at the correct time and to depend upon the high injection pressure for atomizing the fuel.

In FIGURES 15, which are merely schematic illustrations of a representative engine and mechanical or solid injection system, when a plunger 42 is at the bottom of its stroke, as shown in FIGURE 3, fuel will be supplied, as by a transfer pump (not shown), into the chamber 50 above the plunger through a conduit 51 and an inlet port 52, this fuel also filling the so-called helix chamber 54. At the proper time in the cycle of each cylinder, the plunger 42 will be moved upwardly by a lobe on the cam shaft 40 to seal the inlet or bypass (control) port 52, as shown in FIGURE 4, at which time the fuel in the chamber 50 above the plunger and in the helix chamber 54 will be pressurized to open the check valve 46 and communicate its pressure to the residual fuel trapped in the discharge conduit 44 leading to the nozzle 32. The same action is repeated at the check valve 56 in the nozzle 32, and the fuel will be sprayed through the nozzle and into the precombustion chamber 34 and then to the combustion chamber proper 58 above the piston 18.

The end of the injection period occurs after the inlet or bypass (control) port 52, as the case may be, is uncovered by the helix chamber 54 formed in the plunger 42, as shown in FIGURES 2, 5 and 6, because the high fuel pressure above the plunger 42 will be released through the port 52. The duration of the injection period is determined by factors such as the design of the cam shaft 40, the location of the inlet port 52, the distance from the top of the plunger 42 to the control edge 60, the rotational position of the plunger 42, etc.

All of the above described structure is well known in the art, as are many possible variations of the structure shown by FIGURES 15, which are intended merely for purposes of illustration. Those skilled in the art will recognize that the location of the inlet (control) port 52 and the rotational position of the plunger 42 are such as would obtain for maximum fuel delivery, as during maximum load conditions. In other words, as shown in the figures, the fuel injection pump 38 is set to deliver a maximum amount of fuel to the engine.

Referring now to FIGURE 2 for additional details of construction, it will be seen that each plunger 42 reciprocates through a gear 62 which is fixed axially by any means such as spaced shoulders 64 but free to be rotated by a rack 66 usually extending lengthwise within the pump 38. There is a plunger 42 for each engine cylinder 16, and each plunger is fitted with a gear 62. The pump 38 is assembled so that the rack 66 meshes with each gear 62 so that plungers are simultaneously and similarly positioned rotationally by movement of the rack, as indicated by the arrows, thereby delivering equal amounts of fuel to the cylinders of the engine. As is known in the art and shown in US. application Ser. No. 465,422, filed on June 21, 1965, in the name of Lionel D. Thompson,

the rack 66 is normally positioned manually by the operator in accordance with power requirements, the pump 38 having an all speed governor to maintain minimum speed and an over speed governor to limit maximum speed.

It has already been explained that compact, light weight, wide speed range automotive type diesel engines presently under intensive development are beset with serious problems of proper operation under certain conditions of operation such as at no-load idle. It has been proposed by some that such conditions can be corrected or alleviated by providing the engine with a spark plug for each cylinder, thereby improving combustion in a manner similar to automotive type gasoline engines. However, this is objectionable, if for no reason other than that it adds the cost of an ignition system to engines that were originally designed to operate without such systems.

As has been explained, it has been found that excellent results can be obtained merely by changing the angle of the helix or control edge 60 on some of the plungers 42 in the fuel injection pump for a multicylinder engine, in the manner shown in FIGURE 6. At this point, it should be explained that the dotted circles 68 in FIG- URES 36 represent the location of inlet (pumping stroke control) port 52 when the rack 66 has been moved in a direction to rotate the plungers to the engine idle position. That is, the duration of injection will be decreased because the fuel pressure above the plunger 42 will be communicated to the inlet port 52 sooner when the position of the inlet port 52 to the plunger 42 is as shown by the dotted circles 68, as compared to the solid line representation of the inlet ports 52.

It will be noted, in comparing FIGURES 5 and 6, that the uppermost control edge 60 of the helix, as shown in FIGURE 5, has been cut away in FIGURE 6 to pro vide a new double angle control edge 69. Thus, if an eight-cylinder diesel engine pump 38 were provided with four plungers 42 with a helix 60 (greater angle with plunger axis) such as that shown in FIGURE 5 and four plungers 42 with the helix 66 (lesser angle with plunger axis) shown in FIGURE 6, and all of the plungers 43 are rotated by the rack 66 to the idle position, the four cylinders having the helix angle 60 of FIGURE 6 wil receive no fuel, and the engine will idle on the four cylinders associated with the plungers having the normal helix 60, as shown by FIGURE 5.

As already stated, a main problem with these new multicylinder automotive type diesel engines is that noload idle requires so little fuel for each of the cylinders that consistent injection of equal quantities of fuel to each cylinder is difficult and inadequate mixing of the air and fuel results in poor combustion, causing erratic operation and excessive emission.

Obviously, no-load idle operation requires only enough power (fuel) to overcome friction and keep the engine running; this is so whether the engine is operating on all cylinders or some fewer number of cylinders. The governor 45 automatically changes the rack position for no-load idle in an engine in which some of the cylinders are cut off so that some additional fuel is supplied to the cylinders that continue firing. This is due to the fact, as explained in column 3, that the change in helix angles of some of the pump plungers is accompanied by a simultaneous change in rack assembly so that the noload idle fuel supplied to the operating cylinders is somewhat greater than it would be in a prior art pump in which all of the helix angles are identical. Thus, when the governor maintains no-load idle engine speed of the proposed engine, some of the cylinders are receiving no fuel, but the cylinders that are receiving fuel receive somewhat more fuel than they would normally receive if all cylinders were operating. There may, of course, be other equivalent means for cutting off no-load idle fuel to some of the cylinders and at the same time increasing the no-load idle fuel to the remaining operating cylinders. However, increased regularity and efiiciency of combustion due to the additional fuel, resulting in a higher combustion chamber temperature, makes it possible to obtain good low speed operation without supplying twice as much fuel to four firing cylinders of an eight cylinder engine, for example, as it was necessary to supply to each cylinder when all of the cylinders were firing. Thus in an eight-cylinder engine in which four cylinders are cut out, the result is a net reduction in the amount of fuel supplied during no-load idle operation, as well as highly desirable reduction in emission of unburned fuel through the exhaust system.

It would be possible to accomplish a similar result by cutting away a portion of the helix control edge in the vertical direction, as shown by the dotted line 70 on FIGURE 2. However, it was found that this resulted in a tendency of the engine to surge in the initial transition from no-load idle to full-load operation, and experimentation proved that it was preferable to cut away the helix on an angle, as shown in FIGURE 6. While the cylinders that were cut out at no-load idle may experience inefficient combustion during such initial transition, this is of a very short duration during the normal operation of a truck equipped with such an engine, so that the emission level is negligible. Furthermore, such a condition is much preferred over the surge that would result from trimming the helix 66 away vertically.

It should be apparent that the helices or control edges 60 and 6%) on the firing cylinders and on the nonfiring cylinders, respectively, which may be in any combination, not necessarily four and four in an eight-cylinder engine, may be shaped to give any desired performance. At any rate, an engine and fuel system embodying the invention operates noticeably more smoothly at no-load idle conditions, as compared to an engine in which all cylinders fire during no-load idle operation. Also, fuel economy is improved and exhaust emissions are reduced. Continued development of light-weight, compact, low inertia and wide speed range automotive type multicylinder diesel engines, without the problems first mentioned above, is enhanced by the invention.

While a preferred embodiment of the invention has been shown and described with such clarity as to enable anyone skilled in the art to practice the same, it should be apparent that modifications may be possible within the scope of the invention, and no limitations are intended except as recited in the following claims.

What I claim as my invention is:

1. A fuel injection pump for a multicylinder engine, said pump comprising a plurality of fuel cylinders each individually associated with an engine cylinder and each having a control port, a cylinder plunger both rotatable and reciprocable in each of said fuel cylinders, each of said plungers having formed thereon a chamber with a control edge inclined with respect to the plunger axis, the intersection of a control edge with a control port determining the end of the effective pumping stroke for each plunger and thus the quantity of fuel pumped thereby, the fuel supply range of at least some of said control edges being from full load to no-load idle engine operation, engine means for reciprocating said plungers in timed relation to the operation of the engine cylinders and common means for simultaneously rotating said plungers to vary the effective stroke thereof, said some of said edges having a different inclination with respect to the plunger axis than the remainder of said edges.

2. A pump such as that recited in claim. 1, wherein said remainder of said edges have a first inclination in the full load range and a second different inclination in the noload idle range of engine operation.

3. A pump such as that recited in claim 2, wherein the. inclination of said some edges and said first inclination are such as to change the quantity of fuel pumped at substantially the same rate and said second inclination is such as to change fuel pumped at a greater rate.

4. A pump such as that recited in claim 2, wherein said second inclination is such that no fuel is supplied thereby at engine no-load idle operation.

5. A pump such as that recited in claim 4, wherein said common means is manually controlled and wherein a governor responsive to an engine operating parameter is provided to modify said manual control.

6. A diesel engine characterized by a compact, low inertia design and capable of operation over a wide range of speeds and loads wherein the no-load idle speed may be on the order of A; the maximum speed, said engine comprising a plurality of cylinders, means for connection to a source of fuel and a fuel injection pump, said pump comprising a plurality of fuel cylinders each individually associated with said engine cylinders and having a control port, a cylindrical plunger rotatably and reciprocally mounted in each fuel cylinder and having formed thereon a chamber with a control edge disposed at an angle to the direction of plunger reciprocation and cooperating with said control port to vary the quantity of fuel pumped by each plunger over a range of engine operation from full load to no-load idle, engine means to reciprocate said plungers in timed relation to the operation of said engine cylinders, common manually operated means for rotating said plungers, said angle of some of said edges being different from said angle of other of said edges, whereby when said common means rotates said plungers in the decreasing load direction, some of said engine cylinders receive progressively decreasing fuel until they receive no fuel at no-load idle engine operation.

7. An engine such as that recited in claim 6, wherein engine load responsive governor means is operative to position said common means at no-load engine operation so that the engine cylinders receiving fuel at no-load idle receive more fuel than they would if all engine cylinders were receiving fuel.

8. An engine such as that recited in claim 6, wherein said edges are disposed at angles such that some of said plungers change fuel supply upon rotation thereof between full load and no-load idle engine operation at a rate different from the remainder of said plungers.

9. An engine such as that recited in claim 6, wherein said edges are disposed at angles such that some of said plungers have a constant rate of change of fuel supply while the remainder of said plungers have a changing rate of change of fuel supply.

10. An engine such as that recited in claim 9, wherein said changing rate of change of fuel supply is such that no fuel is supplied at no-load engine idle operation.

11. An engine such as that recited in claim 9, wherein said changing rate of change of fuel supply is greater at the low engine load range than at the full engine load range.

12. An engine such as that recited in claim 9, wherein said remainder of said plungers have said edges disposed at a dual angle between the full load and no-load idle ends thereof such that there are two distinct rates of change in fuel supply.

13. A fuel injection pump for a multicylinder engine, said pump comprising a plurality of fuel cylinders each individually associated with an engine cylinder and each having a control port, a cylinder plunger both rotatable and reciprocable in each of said fuel cylinders, each of said plungers having formed thereon a chamber with a control edge inclined at an angle with respect to the plunger axis, the intersection of a control edge with a control port determining the end of the effective pumping stroke for each plunger and thus the quantity of fuel pumped thereby, the fuel supply range of at least some of said control edges being from full-load to no-load idle engine operation, engine means for reciprocating said plungers in timed relation to the operation of the engine cylinders and means for simultaneously rotating said plungers to vary the effective stroke thereof, certain of said edges having a different angle of inclination with respect to the plunger axis than the remainder of said edges,

said remainder of said edges having a first inclination angle in the full-load range and a second different inclination angle in the no-load idle range of engine operation, said second angle being such that no fuel is supplied thereby at engine no-load idle operation and such as to begin reducing fuel at a greater rate than said first angle prior to attainment of no-loa'd idle engine operation so as to prevent a sudden complete cut off of fuel as supplied by said first angle.

14-. Fuel feeding mechanism for multicylinder internal combustion engines comprising a plurality of fuel plungers each individually associated with an engine cylinder, means for regulating the fuel delivery of each plunger, and common operating means for said fuel regulating means, said regulating and operating means being arranged to provide substantially equal fuel delivery from each of said plungers at all loads between full-load and light-load and to reduce the fuel delivery of certain of said plungers within the range of adjustment of said operating means between light-load and no-load idle engine operation gradually but at a greater rate than the fuel reduction rate of the remainder of said plungers, whereby said certain plungers supply no fuel at no-load idle operation and engine idle is sustained only by fuel from said remainder of said plungers and whereby engine operation through the range of said different rates of fuel delivery is free of sudden cut off and re-establishment of fuel delivery by said certain plungers.

15. A fuel injection pump for a multicylinder engine, comprising a plurality of pump cylinder-mounted fuel plungers each individually associated with an engine cylinder, fuel control means for each plunger comprising a chamber formed thereon and having an inclined control edge cooperating with a 'fuel return duct formed in said pump cylinder around said plunger to determine the effective pumping stroke of said plunger, said plungers being rotatable to vary the point at which said return duct becomes eifective, the effective inclined control edge of certain of said plungers having greater angles of inclination differing from that of the inclined edges of the remaining plungers, and a common means for rotating said plungers simultaneously and in the same direction, whereby the fuel delivery of said plungers having the said control edges with greater angles of inclination are cut off at a point in the movement of said common operating means still within the control range of movement of the remaining plungers.

16. A fuel injection pump for a multicylinder engine intended to idle on less than all of its cylinders, said pump comprising a fuel cylinder for each engine cylinder, a control port in the wall of each fuel cylinder, each fuel cylinder having a rotatable and reciprocable plunger therein formed with a control edge contoured to be inclined with respect to the plunger axis and cooperating with a control port in determining the effective pumping stroke of said plunger, means for reciprocating and simultaneously rotating said plungers, each of said control edges supplying substantially the same quantity of fuel in the full-load range, said control edges for the engine cylinders operating at idle being contoured so as to supply fuel at engine idle and said control edges for the engine cylinders not operating at idle being contoured differently in the idle range thereof so as to gradually reduce fuel upon decreasing load until no fuel is supplied thereby at engine idle.

17. A pump such as that recited in claim 16, and including further an idle governor operative to set said common rotating means whereby said engine cylinders operating at idle receive more fuel than they would in an engine in which all cylinders operate at idle.

18. A fuel injection pump for a multicylinder engine intended to idle on less than all of the cylinders, said pump comprising a plurality of fuel cylinders each individually associated with an engine cylinder and each having a control port, a cylindrical plunger both rotatable and reciprocable in each of said fuel cylinders, each of said plungers having formed thereon a chamber With a control edge inclined with respect to the plunger axis, the intersection of a control edge with a control port determining the end of the eifective pumping stroke for each plunger and thus the quantity of fuel pumped thereby, engine means for reciprocating said plungers in timed relation to the operation of said engine cylinders and common means for simultaneously rotating said plungers to change the control edge-control port relationship and thus vary the effective stroke thereof, the inclination of some of said control edges being such as to have a fuel supply range from fullload to and including no-load idle engine operation and the inclination of the remainder of said control edges being such that the fuel supply range thereof is from maximum fuel at full-load to no fuel at no-load idle engine operation, the inclination of all of said control edges being substantially identical in the high load range and the inclination of said remainder of said control edges being greater than the inclination of said some of said control 10 edges in the low-load range, 'Whereby said some of said control edges continue to supply fuel at no-load idle engine operation and said remainder of said control edges gradually reduce fuel at a greater rate than said some of said control edges and completely shut off fuel therefrom when no-load idle engine operation is reached.

References Cited UNITED STATES PATENTS 1,967,10 1 7/1934 Rasshach et a1 1034 1 2,3 17,022 4/1943 Benjamin 123-440 3,308,680 3/ 1967 Sherrick 123-55 LAURENCE M. GOODRIDGE, Primary Examiner.

US. Cl. X.R. 123-32, 139, 140 

